Better to have have too much tea and not enough pots than the other way around.

As others have mentioned shincha is top of my list when thinking about freshness, keeping an eye on the shincha thread each year is probably the best way to research vendors.

Some pre-ming long jing would also be a good bet. I find Jing tea shop has a nice balance of quality and price for Chinese greens. Their everyday greens are often excellent for the price and higher end greens can be ordered by the ounce.

i believe their tea sources are shared by a guy who sells at Borough Market
i've lost the link to his site tho .. and more importantly, the site/name of a lady in Notting Hill Gate who has both Chaozhou pots and DanCongs

Fortnums is kinda fun to buy tea at. They have Tie Guan Yin, amongst other teas, in vast jars behind the counter, and they will get em down for u to sniff.

they dont wrap yer tin of tea in brown paper and strongstring [with a loop to carry it by] anymore tho, like back in the day